1. Field of the Invention
The present invention relates generally to a transmission system for local subscribers, the system being comprised of a central office terminal and a local subscriber side remote terminal, both connected between a central office exchange and local subscribers, and more particularly, to a testing system for the local subscribers.
2. Description of the Related Art
In a usual telephone communication system, a central office exchange and the respective subscribers are connected directly to each other, but in a particular telephone communication system in which local subscribers are located far from the corresponding central office exchange, a subscriber side remote terminal is installed in the vicinity of these local subscribers. Namely the local subscribers are connected to the central office exchange via the subscriber side remote terminal and the central office terminal, for voice signal communications.
Such telephone communication system must be, of course, tested, to maintain the functions thereof in a normal state. Namely, a test is carried out to determine whether or not a fault exists between each subscriber and the subscriber side remote terminal. There are two kinds of tests carried out; a remote test and a local test. The remote test is conducted by a remote test equipment located at the central office, and the local test is conducted by using measuring apparatus at the remote terminal site.
In detail, in the remote test, a control signal is sent from the remote test equipment and transmitted to the subscriber side remote terminal, via the central office exchange and a two-way transmission line connecting these two terminals. At the subscriber side remote terminal, upon receipt of the thus-transmitted control signal, the ends of each local subscriber line are switched over by respective remote test switches to a common test line arranged so as to connect the remote test equipment separately to the two-way transmission line, whereby a remote test is carried out for each local subscriber line.
If a line fault is detected by the above remote test, then the end of the faulty local subscriber line is switched over by the remote test switch from the test line to the measuring apparatus, and then a local test is carried out to find the precise location of the fault in the local subscriber line, and investigate same.
The above-mentioned test system for local subscriber lines will be explained hereinafter in more detail with reference to the Figures. Note, this system has been proposed in U.S. Pat. No. 4,270,030, to Stephen J. Brolin et al., and assigned to the Bell Telephone Laboratories, Incorporated.
The test system of U.S. Pat. No. 4,270,030 does function well for the maintenance of the local subscriber lines, but in practice, some problems arises during the test, as explained below.
The local test is carried out not only when a line fault occurs, but also when making periodic checks on each current subscriber line. Where such a local test is carried out the remote test switch is switched over to connect the measuring apparatus by disconnecting the end of local subscriber line from both the subscriber side remote terminal and the test line. Under these circumstances, if a remote test is carried out at the same time, the remote test equipment will erroneously determine that a line fault exists in the local subscriber line that has been disconnected for the local test, even though in fact, there is no fault in the line. This erroneous determining of a fault by the remote test equipment is the related problem.
To overcome this problem, at present the maintenance operator at the remote terminal site calls the remote test equipment site and asks the operator there not to conduct the remote test with respect to the local subscriber line now being subjected to a local test.
Nevertheless, if the maintenance operator forgets to call the remote test equipment site, the remote test is started as usual, and thus the aforesaid erroneous determination is made by the remote test equipment, which then issues an unnecessary alarm signal.